For a large majority of my time in bitcoin, I have been considering 4 years as a minimum investment timeline, and if people invest less than 4 years then they are trading rather than investing, and sure, even 4 years might not guarantee profits.. but at least a minimum of 4 years can provide a framework for someone who is not sure about his timeline to consider whether bitcoin is a good investment for him, such as someone who might be in his 70s, he might have some ballpark ideas that he may well need the money within a certain amount of time, such as 4-10 years, but then he is not sure, but he still might be o.k. with locking up his money for at least 4 years, even though he does not exactly know when he might need it.
It's your personal experience that matches with what data shows for the majority of Bitcoin investors but anyway I am thankful for your shared information that is truly helpful not only for me but also the others.
The HODL Camp map shows nearly the same information as what you shared.
https://hodl.camp/This map provides a valuable information of the HOLD line with a minimum hodling period of 5 years and 1 month. This recommended hodl time is not considerable different to your suggested one of 4 years.