I have a lot of trouble telling people when I'm having problems, or feeling burdened. (It's especially hard to confront a person who is causing me to feel troubled.) I don't want to burden them with my own concerns. It feels like a selfish imposition.
But ultimately when my friends do find out that I've been unhappy or upset or whatever, their response is never, ever "Thanks for being a good friend by keeping that to yourself and not messing up my life." It's always "Why didn't you tell me before??"
Why didn't I tell them before? Because I was afraid to show them where I really was. Because I was afraid to impose. Because I was too proud to be really known. Because I was too selfish to be a true friend by being my true self, which is inherently vulnerable. Because I didn't trust them to be real friends by loving me even when I'm not in a good place, even when I've made bad decisions, even when I'm receiving from them instead of giving to them. Because I was too proud to admit I needed help. Because I scorned their ability to help me. Because I didn't believe in community.
To pretend I have it all together is to choose the death of loneliness, of having my heart shut up so that it withers and hardens until (as C.S. Lewis says) it is no longer a heart. It may not be breakable in that state, but it is no longer mendable either.