This is a great question, and one that is central to the whole process of transitioning.
Firstly, I don't think we get past all our fears, but just decide that we must face them (but not all at once). It's cliched, I know, but it's all about taking one step at a time; that is small, manageable steps. I think an initial phase of "stealth" transition where you adjust your weight; start HRT; make cosmetic changes (such as facial laser-hair removal for trans women); increase the frequency of presenting yourself in public as your preferred gender, but not necessarily "make the giant leap" of announcing your transition to everyone. I will never forget the instant I decided to transition, and made an appointment with my gender clinic. In my mind, the words, "Okay, let's do it" marked that instant.
This initial "leap", where in your own mind you have reached a tipping point where you certain that you want, indeed that you need to transition, will in time lead inevitably to the final leap where you make it generally known that you are transitioning. I'm on the verge of this second and most difficult leap (which is possibly the one you're actually referring to). For me, my two fears are the effect my announcement will have on those I love followed by the effect it will have on my employment. I still present as a male at work, but have to wear a sports bra to hide my breasts (I had breasts even before I started HRT just over three months ago, and they have grown even larger since then). Clearly, I can't keep this up for ever.
The calculus of deciding when to make the final leap (i.e. the grand announcement) is complex, and depends on your personal circumstances. But the surety and determination that I have made the right decision to transition, not to mention the inner peace it has brought, will, I am sure, help me get past my final fears.