Could we have been more attentive?
Could we have had that meeting earlier to iron things out?
Could we have just told the chef it wasn't good enough to take out?
Could we have made it in sooner this morning?
Could we have done more to be ready on time?
Could we have avoided winding that person up?
Could we have thought about that more before we went ahead?
Could we have squeezed in that extra table?
Could we have checked that it was cooked through properly?
Could we have double checked that bill was correct?
Could we have done better?

It's easy to say; 'Perhaps not'.
The real question is; 'Why not?'