Selling or holding your cards mainly depends upon what type of card you are holding on to and mainly if you are patient enough to get the most out that such item. If you are patient the card may pay out incredibly even enough to turn your life around or may even become worthless, it all depends upon what type of card you are holding on to what is its current condition how many of them were made and is it of a mainstream player or not.
We can take the example kobe bryants cards when recently the legend died in a helicopter crash , items related to him have increased in price numerous times because they have become more unique as they were before, Also we can take the example of lebron james cards which got some setbacks in their price following his remarks about the hongkong protest, so many things play a pivotal role in the price spike or plunges in this business which you need to look put for before investing or divesting in these products.