Your desire may not (even if it is good in itself for many) be the desire God wants you most to have. God calls you, you don't call yourself.
I'm aware that we don't call ourselves, but my sources say that God calls everyone who has this desire. Which makes sense. The religious vocation is not like the priestly vocation, reserved only to a select elite, but is rather a general invitation that's open to everyone who wants it. All that matters is that the desire be genuine--a true desire for one's own sanctification through the religious state. Genuine desire is always accompanied by a vocation, and this vocation is always from God. It's as simple as that.
No, it's not as simple as that because you admit that it's a three-way process: (1) God, (2) the receptive individual, and -- (3) the instrument of God, the religious institution discerning from their end the appropriateness of the candidate. Your "source" is not credible if your "source" is suggesting that knowing whether one has been called to religious life or the priesthood won't really know that until the moment of or after ordination.
Religious bodies have a right not to waste their time and money. It's not a matter of just a ready heart wanting to serve God. There are particular requirements for the job that are evident enough prior to beginning the seminary training, which is expensive and which often the candidate himself cannot afford -- thereby requiring donations from others and/or the resources of the institution itself. They will not be throwing their money on an entire class of experiments for 7-10 years of seminary training or many years of religious formation. Either you misunderstood your "source," or your source has misled you into believing that "everyone" has a call if only he or she is willing.
Temperaments in a more particular sense than either the Four Temperaments or personality traits are an essential aspect of discernment. Most people, including many people in the pre-formation discernment process, have a vague idea about what this kind of life entails, but few really understand the level of sacrifice involved. A sacrifice that "goes against the grain" in a fundamental way -- such as a resistance to particular kinds of detachment, or detachment in general -- is a contraindication for religious life. The vast majority of Catholics have attachments. It's just the object of those attachments that differs from person to person.
I'm not talking about attachments to material things but attachments to:
independence
privacy
basic control over one's time, especially whatever is considered "not-on-the-job" time
sleep
friendships -- past, present, future
locations
family, and holidays celebrated with family
personal preferences/lifestyle choices of any kind (food, types of associates, climate, etc.)
stability of position/role
predictability
recreational opportunities
Poverty, chastity, and obedience, on the literal level of those, can sometimes be the relatively "easy" part, compared to the divestment of the kinds of freedoms that we do not realize we deem "essential" or certainly "expected." Stripping of attachments is part of both poverty and obedience, depending on the category.
People imagine they can live without these and other attachments, but often they do not know themselves well enough -- from age or emotional maturity and self-awareness -- to consider what's ahead of them and whether they have "the right stuff." That's why older and wiser men and women are put in the position to judge the probable level of detachment of the inquirer, a detachment that is visible not just from the candidate's words and personal history but his or her recent choices, activity, lifestyle -- spiritually and earthly. It is not merely a subjective discernment
and people better respect the fact that God calls everyone; I know in some absolute way that I am called. No, you don't. It is not a matter of private judgment that overrides what a Vocations Director can judge himself or herself. No one on SD is in that position, but a VD is.
Is the candidate psychologically mature for his age? One aspect of maturity is realism and being down-to-earth, not an idealist who expects others to simply trust his or her impulses.
Is the candidate spiritually mature for his/her age and for the perseverance that will be essential for the long haul in religious life? I explained in other posts the signs of that spiritual maturity, which are judged not by the candidate but by others,
before entrance. Spiritual maturity does not refer to perfection or advanced virtue: all of that comes with proper formation and response to formation. It refers to (a) awareness of what's involved in the spiritual journey; (b) awareness of what's involved in religious life; (c) signs today that the candidate has been and still is, consistently, working on that spiritual journey in a way qualitatively different from pious laypeople; the candidate is singularly and wholeheartedly focused on this on his own initiative. All later successful candidates I have known have shown these observable predispositions which set them apart. And that is only one part of the discernment.
The religious vocation/lifestyle is basically missionary. You go where you are sent, when others want you there, regardless of whether or not you think yourself ready, do not like the assignment, will not like the assignment, believe you are suited to the assignment, will find it an enormous Cross for any reason (physical discomfort, people unlike you in background, a role you've never done or dislike, isolation from everything you love, etc.). Your source is wrong: Not everybody has equal capacity to accept this lifelong missionary role. It requires:
observable maturity, now, not just later
exceptional motivation not common to the entire human race
ability to sacrifice, observable now
unusual ability to discipline oneself, with evidence of that (e.g., the difference between the two male candidates I described earlier)
awareness of the level of detachment required lifelong, with evidence of ability to detach
nowno major vice that is so crippling right now that one would be beginning the process behind other candidates; an example in my earlier comparison was the persistent Sloth of one vs the persistent spiritual diligence of the other; I know the latter person's faults, by the way, and I know he will have to work on those in seminary, but clearly he has the motivation and discipline the other lacks.
And one could have all of the above but simply not the role of missionary -- in which case, the candidate is unsuitable for religious life, no matter how personally holy.
God works with what we have and loves us all infinitely but knows that we are more suited to certain roles than others. There are parallels in secondary vocations as well. Someone drawn to a life of secular service will not be equally good as a teacher, nurse, doctor, or social worker. The roles and capacities are different. A person who loves to work out of doors will not be equally good as a forest ranger and a landscape gardener: different roles and capacities.
Because God calls each of us to total love of Him does not mean that anyone or everyone has the capacity for religious life. The Church does not believe that; religious orders do not believe that. It is completely possible, however, for each of us to love God as completely in non-religious life as we would if we were to have a true religious vocation.