Never
Don't you think it is such a waste to live life half-heartedly?
No matter who you love, you will still find sadness and pain in between.
No matter how good you are at anything, you will still deal with failures and problems all along.
No matter who you trust, you will still face lies and betrayals sometimes.
No matter who you are with, you will still meet loneliness and emptiness from time to time.
Why should you bother to worry and protect yourself so hard then? Rather than building a wall so high, why don't you grow your wings instead?
Rather than fencing your glass heart, why don't you just break it into pieces and fix it like a puzzle?
Sometimes, it is good to not knowing where the pieces of the puzzle are, giving you time to realize that maybe you don't really need to know the whole picture of your puzzle.
And maybe you never will, anyway.