Due to my schedule I have not posted for a while. When I saw this article, I just had to comment on it.
What this article is basically is telling people are two things about investing: 1) don't trade on emotions (this is good) and 2) buy and hold (this is not a good strategy).
They also try to spin the bad by saying this is what the pros do. Well, I know a few pros, along with many very successful investors, including Sean Hyman (a pro and a successful investor), and this is not what they do.
If the fundamentals or technicals indicate you should sell, then sell. No one has a crystal ball when it comes to trading, but there are enough indicators, along with keeping up with geo-political events, that can help you know about when to buy or about when to sell.
I tend to hold on to my stock investments since I don't like to have to pay taxes on my gains, but it's a much better alternative (i.e. pay taxes on your gains) than going down with a sinking ship and either losing more or losing your gains. It's just never a bad thing to take profits and lock them in! Plus, if you've made a gain, then sell, then something changes that signals you should re-buy the stock, you can get back in as quickly as you want to into that same stock (i.e. it is not a wash sale). A wash sale is when you sell a stock to limit your losses and, therefore, claim a loss (so you have lost money in the stock) and you try to buy back into that stock within 30 days.
Over the last 3 weeks, I have sold my entire stakes in 3 different stocks, which is somewhat rare for me. I will usually just trim my investment in a stock (i.e. sell some but not all) when something underlying in the stock changes for the worse or other factors affect it (e.g., governmental agency, geo-political events).
If your stock investment is in a qualified account (e.g., IRA, 401K), then there is no such thing as a wash sale since you don't pay taxes on the gains or claim losses until you take it out, hopefully, after you are 59 1/2, to avoid the 10% penalty. When you take a distribution from an IRA or 401K, then the entire amount is taxed as ordinary income. Tax laws change regularly, so please consult the proper professionals instead of taking any tax advice from me. It's been a while since I've researched taxes related to these types of accounts.
Net/net: don't be afraid to sell any particular investment. Knowing when to sell is just as important as knowing when to buy (meaning knowing about when to sell and about when to buy) in order to build wealth.