Almost anyone should be able to figure out whether they have an extra $10 or not. If they cannot figure it out, then they have to figure it out...so once they figure out that they have an extra $10 they can get started, and they can sort out the other aspects of their potentially messy finances and/or psychology as they go. Position size can do a lot in terms of both starting out and also not overdoing it so that there are abilities to figure out an appropriate level of aggressiveness. I would thing that most people are going to start out investing into bitcoin in a non-aggressive way and work their way up towards being more aggressive, unless they happen to already have a pretty good grasp on their finances and they can understand and appreciate the strength of bitcoin's investment thesis from the start.
$10 constant investment will amount to little in the long run and almost a messy way to start up a bitcoin investment, I think also that for anyone to arrive at a successful investment position one needs to be aggressive a bit, at least that will help us to be able to take some aggressive financial decisions that can help us to arrive at a good investment position faster.
Investing a low amount like $10 as mentioned by members sounds like a joke considering Bitcoin's current value.
Starting a bitcoin investment with $10 isn't a bad bet, no one is saying to stay at that price indefinitely, and also @JayJuanGee said 'extra $10' making that price at the very least the lowest anyone who what to invest in bitcoin should go, if at the end of the day your discretionary income only amounts to $10, then invest it! while at the same time looking for ways to increase that minimum. This way a person can avoid procrastinating on when to start investing simple because they can't afford to do away with more than $10 at that time.