"That's good, but..." (reason why it's not)
"Yes, but..." (no)
"I believe, but..." (I doubt it)
Many times when a period would suffice, we can't help it, we still say 'but'.
Leave out the negative 'buts'. Mainly the ones that pull down good ideas, zealous spirits or 'aha' moments.
Instead, put it to good use.
"It's a stretch, but it's possible"
"I'm tired, but it's going to be worth it"
"Life is hard, but God is good."