The Volkswagen Caddy - However Big Your Ambition survey of a thousand SMEs revealed that mistakes and bad decisions cost UK businesses an average £2,340 every year.
Not taking advantage of an opportunity was the number three business mistake, followed by offering too much of a discount and hiring a friend.
Sixth place in the list went to taking on a relative to carry out a role in the company; while firing someone and later realising they shouldn't have been giving the boot was at seven.
Trusting the wrong person or business partner was eighth in the list, with investing in equipment which didn't do the right job and ignoring good advice completing the top ten.
Over a third (35%) of owners say they have let their heart rule their heads at some point, with 61% of those saying the decision proved detrimental. More than half of those (56%) say they even lost money because of it. Another one-in-ten admitted their company's reputation was affected.