It doesn't matter how confident you are, or how much you trust yourself, ---- happens!
How confident are you that there isn't a cable run outside of the safe zones that you might drill in to?
How much do you trust yourself to know exactly where a pipe has been randomly buried in the plaster where you need to drill a hole?
I have a good level of confidence in doing my job properly, but have still managed to drill through various cables and pipes, and one painting.
I've nicked a burglar alarm cable and had the police turn up, and had a couple of near misses with sprinkler heads.
I've seen someone hit a fire alarm cable and face a £1k repair bill, plus making good.
Insurance cover is, in my opinion, essential before picking up your tools.