If bitcoin's price decreases I will buy more while it's low then wait for the time that it will increase again to sell and at the same time I am going to invest to altcoins.
It is just normal if sometime the price of bitcoin drops because it is the economics. Not all the time it is in its peak, but if in case that happens I think what we should do is just hold it first. Take a look at its performance for the coming weeks. In case the price continue to drop then dig deeper. Check some factors why the price drops and if you found out the problem check then if it is just a minor problem or a big one. From then you can decide if you'll gonna sell it. I think it is better to hold it and have trust in bitcoin.