This will result in at least two kinds of errors. First, fear of losing your unrealized gains on the great picks in your portfolio will make you sell too early. Think of the man who sold Infosys after the IPO because it had risen by 50% from its IPO price so quickly.
Second, it will make you reluctant to take losses on the bad picks, even though better stocks to switch into are clearly available.
Learn to cut the weeds and water the flowers, and not the other way round.