Regret is a useless emotion. ignorance, well, that's different. The Japanese have a concept known as 'Kaizen'. it is a philosophy of continual improvement. things happen, but, they cannot happen any other way, and it should be obvious how ridiculous it is considering the ideas of what should have been, or what 'should have' been done. However, to move forward without regard or retrospect for the past is ignorant and blind. Perhaps, a good way to appreciate a given situation is like a knife and it's condition. A sharp knife will cut clean, straight and through, it is only this because it is prepared and ready, the best it can be for a given situation. Pablo Picasso said when asked:
"How do you create the perfect painting?"
"Well that's simple. Make yourself perfect, then paint as normal."
furthermore, when things do not conclude as you might have planned them to, maybe you should relax in the knowledge that they rarely do, as Robert Burns suggested in 1785:
"But Mousie, thou are no thy-lane,
In proving foresight may be vain:
The best laid schemes o' Mice an' Men,
Gang aft agley,
An' lea'e us nought but grief an' pain,
For promis'd joy!"