Give 110% to everything important you do. The extra 10 % is usually the clincher. After giving your full dedication and going the extra mile you need to move on. If things still don’t work out understand deeply the reason so you learn from the experience and apply the learning going forward.
Usually, things do not work out because either the trust and rapport is not strong or you have not understood and solved the real problem. Sometimes it could be that you have not articulated the solution immaculately or been able to understand and surmount the objections. At other times it does not work out because you make it a problem between you (win-lose) instead of making the problem before you (win-win).
However, once you have done all of the above then you can move forward in peace. Do your best, leave the rest!