You just know when something is "it". In the same way, you also know when something isn't. This rule applies to shopping for a dress or a pair of shoes, getting into a relationship, figuring out if a career move is a go or not.
Call it intuition or gut feel - basta, you just know.
There is a difference between gut feel and reckless impulse. Let me attempt to define the difference. First is in context. Gut feel is a subconscious, somewhat psychic self-preservation mechanism that aims to veer away from harm and toward good. Gut feel comes in the face of major decisions to be made. Reckless impulse is a submission to the id, that hedonistic part which wants to please the senses. The second difference lies in the consequence of following one over the other. Following gut feel ultimately results in a desirable outcome. Acting on reckless impulse elicits temporary feelings of pleasure which later turn into guilt and remorse.
God knows I've had my share of gut feel-led and reckless impulse-influenced decisions. It takes a quiet, unperturbed, non-judgemental state of mind to make sound gut feel calls. And when you have a tendency to people-please like me, it isn't easy. It requires constantly retreating into oneself, getting rid of the hang-ups, unloading the baggage, and asking the really tough questions and answering them with brutal truthfulness.
I honestly believe that a life well-lived is one that is 40% rational thinking and 60% heart-led action. Why? Because if the rational part took over, we would constantly be afraid to take risks. I'm not saying do away with it completely, obviously. But having the courage to go beyond comfort zones needs more heart than logic.
Sometimes, you gotta stop thinking, and just start living.