We all have regrets and most won't hold us back. In letting go we acknowledge a lesson learnt and maybe feel a bit guilty or annoyed that we didn't see the problem at the time - hind-sight is an annoying teacher. Give your past self some credit - they weren't as wise as you are now!
If you’re regretting past errors or fear repeating them, try to move on. The past is most definitely not a guide to the future but your successes might be!
Not all your IDEAs will succeed. Move on and create some more. Which sounds like classic advice for entrepreneurs…
Winnie-the-Pooh has an interesting if poignant perspective on this - at the end of A. A. Milne's original version Pooh and Christopher Robin walk off to 'the enchanted place, and there we leave them'. Which is a statement about the end of childhood, leaving it behind but not forgetting it. It is now done, but still exists - we've learnt from it but are moving on, can't revisit (arguably shouldn't try).
A poem "In Passing" by the late Lisel Mueller (thanks to Maria Popova for the reference) captures the bittersweet process of change wonderfully, from the forward to her book:
How swiftly the strained honey
of afternoon light
flows into darkness
and the closed bud shrugs off
its special mystery
in order to break into blossom:
as if what exists, exists
so that it can be lost
and become precious.