The brand name was good, customers recognized it business was growing. But I kept putting off registering it thinking 'it's a waste of money'. Trademark registration costs 500-1000 lira, if you hire a lawyer it's 2000-3000.
Two years later a similar company opened the name was almost identical. Customers were getting confused. I thought about suing but the lawyer said: 'since you didn't register you're weak in court. Even if based on common law, it's hard to prove.' So I quickly got it registered and sent a cease-and-desist letter to the other party.
Result: registration took 5 months (slow in Turkey) but there was a lot of stress and customer confusion. Eventually that similar company was forced to change its name. But if I had registered from the start, this hassle wouldn't have happened.