Its pretty much explained by “breaking the ice” there is a stage of a relationship where both people want it and they aren’t sure how committed the other is. This leads to them wanting to take a risk and advance the relationship but fearing the chance of not doing it properly and failing.
From my experience all you can do is take a leap and say what you want to say and after that you can relax and joke about how nervous you both were. Unless you get rejected then you go home and cry in a bubble bath.