What´s wrong with a big ego?

Self worth and self esteem are not the same as ego. Self esteem and worth are positive and healthy. Ego is a selfish trait that puts you in a position of false superiority.

Not one damned thing! Having said that, however, I will say that 9 times out of 10 it's purely self-aggrandizement with no INTELLECT to back it up! It's that ole saying, "Better to keep your mouth SHUT and leave your intellect in question than to open it up and remove all doubt!" (or something like that)

It often results in an inability to learn from your mistakes. How can you correct them if you don't think you've made any? I've seen more than one talented person ruin their career by refusing to listen to those that ranked below them. They didn't want to show any signs of weakness. They were afraid it might undermine their authority. So they kept repeating the same errors until they were fired.
The people who make it to the top are usually humble at first. They watch and learn while biding their time. The guy with the big ego, on the other hand, will immediately start telling everyone how to do their jobs. He will waste his energy trying to acquire power rather than finding out the best ways to get things done. He will delude himself into thinking, "If only I could get everyone to do it my way then everything will work out." Meanwhile, the humble guy takes advice from the peons. Guess who wins in the end?

to me nothing, if you are pleasant, socialable and at least reasonable.

No one wants to hangout with an egotistical person.

It makes it hard to find a hat that will fit on a swollen head. : )

You must be big enough to fit it.

Go blow up a balloon. Now let it go without tying it up. You can even tie it up and then pop it after if you prefer to do that instead. That's what's wrong with a big ego.

Someone with a big ego is full of hot air with absolutely nothing to protect himself or herself when his or her ego loses hold of the people who are feeding it. In some cases, it may only be one person who is. If someone even dares to "prick" at his or her ego, he or she feels deeply wounded just like that. How dare anyone question him or her?

There's no foundation, no security, nothing. Not even substance. That's like building a house without a foundation. That's like building a chair without legs. That's like climbing a mountain without protection and other things that will help you survive. That's like standing at the finish line when you weren't even part of the race and trying to convince everyone you're the best and you deserve the prize, even though there are other people who deserve it because they actually put in the work and effort to get there.

A big ego is very bad. People who have one need to wake up to reality and see that they are not better than the people around them for any reason whatsoever.