Of course when they sold at cheap price they end up regretting their investment as I can say that bitcoin isn't that predictable based on price movement and differences and of a true 10 year can be considered a sufficient time period for one to hold his bitcoin except for someone that is greed to make some profits while they proceed their holding processes, that result in decreasing the total amount of Bitcoin in their custody.
10 years may or may not be enough. Surely if a person had been investing 5% per year, then after 10 years, he has only invested about 50% of his annual income into bitcoin, so they might not really be in a very strong place with their BTC investment, even after 10 years investing. Of course, 10% would result in a whole year invested and 20% would result in about 2 years of income invested.
This depends on individual plans and foresightedness to have had this long time projections with their investment plans carving out or sparing out their 5 percent per year or annually would also go a long way but then are they really ready to do that as we may say, naturally it's a good point and a very suggestive idea to help foster the accumulation processes..
Of course there are people or investors who are determined to carry out their investment plans through that strategies but on the one way or the other fall out of fate due to some form of unforeseen circumstances or not having sufficient spare cash or a cushion to covers up their unpredictable expenses, something that would make them to start tempering their proposed plans and or their portfolio making them to reduce their percentage that was set and plan for their continuous accumulation process.