Holding bitcoin is not a wrong thing to do. The logic is very simple, bitcoin is the only coin that is being useful in the shops as a first choice for places where it is somewhat legally tradeable. Next the altcoins are all based as copy-cats for bitcoin and their basis of pumping is "second" or "third" to bitcoin - with a delusional belief on it becoming the next bitcoin - we all know that never happens.

Hence you may wish to hold other coins too but that is a personal choice for being bullish on something other than bitcoin. Someone may be bullish on something from a different sector too - dont waste money on altcoins then, move to the other traditional markets.

"Stealing opportunities" - disagree to this. These markets are based on speculation and there are several opportunities. We must admit that we often fail to recognize them.