I thought about posting it in the investor thread, but I think I have asked a similar question before. So now just posting as a comment in this thread.
I have one colleague who is always at work looking into stock websites. I asked him whether he changed his funds regularly.
He told me that he has his stocks only in his pension fund. When he has index funds and the index has risen more than 10%, he switches to a bond-profile with 0 risk. When the index has a big dip, he switches back to the high risk profile with index funds. That way, according to himself, you never lose money. He said he made 25% profit the last two years. This person has a history of getting into high debt because of losing money on the stock market. I think this is his new way of wanting to be into the market, but into a saver way.
It does sound like safe strategy to me, but for me this would be challenging I think. I Norway we pay about 30% tax on profits we make when we sell funds. Currently my funds are on a account where I can postpone my tax paying to the moment I take out the money, which is hopefully after FIRE when I have very little income. In this account, you cannot have bond funds, but we can switch between stock fonds as much as we like. But buying bonds would mean having to pay the taxes on top of my current high salary.
I think that if you sell index funds when the fund has more than 10% profit, you will lose out on the big profits. Like one of my index funds has currently 15% profit. But I do sometimes get a little nervous on having so much stash index funds, as I cannot believe the market will go up forever.
But we are back to the eternal question "is investing in the the stock market smart or not" and in the long run it is supposed to be smart. That is why I have my stash there. If we ever get 8% rent on money in the bank, I will put it in the bank. But I think those days might be over.