Well an investor must not sell when Bitcoin hits seven figures because seven figures is really a long way to go even though Bitcoin is volatile. The only time an investor is suppose to sell is when they have reach their target which is the overaccumulation stage and getting to overaccumulation stage doesn't also mean one can or should sell their investment anyhow but rather it is advisable to sell a little cent of it and while selling you are also investing back little to ensure that cent taking off are not been notice.
Depends in how long the investor has been holding someone that's held for more than a decade is allowed to sell if the person witness bitcoin get to seven figures, especially when the person has reached their target, selling some portions is not prohibited, for such person it's a thing of choice, but it would be unwise for someone who's just getting started, someone who's not even reached a full circle, someone that's yet to meet their target to sell when bitcoin reach seven figures just because they made some profits, seven figure is not the end point of bitcoin it still has the potential to go further so anyone that's not held for atleast a decade should hodl tight and keep building. Anyways for those who take profits when they're ready they can still continue with the DCA to recover back what they've sold and make more profits on the long run as the figures keeps going higher.