Question

Which one is the most obvious reason why trading too much can be bad for your overall return?

		On average, people make bad trades that attenuate returns
		Trading too much entails too much trading costs which hurts the net return
		People who trade too much seek too much risk
		People who trade more suffers more from psychological biases

Answer 1

Trading too much can negatively impact overall return:

2. Due to trading costs - that would be certain since trading volume, is directly proportionate to the trading volumes.

the other points are not obvious :

1. On average people make bad trades - has no basis and is mere supposition
3. People who trade too much seek too much risk - could be the trend, but definitely not an obvious fact
4. People who trade more suffer from psychological biases - generalization, since succesful traders, without biases trade a lot based on mathematical models too.

Hence answer is

B) Due to trading costs.