Stuck in long term investing - What is the Opportunity cost in investing?

I would define Opportunity cost in Investing as the loss of chance of compounding your available investing capital and gain of the next best alternative stocks foregone as the result of staying invested in a losing position held for many years; whether it is due to silly stubborness and cannular conviction.

As the Market changes, and very often sectors are rotated into favour or out of favour. Likewise, we should also be flexible and evaluate the Opportunity cost and continously adjusting the portfolio to the flow of the Market and allowing the effect of compounding to work for us and then accumulating profit to offset against losses.

BTW, it is your money. Who care!