This is true. But investment is by choice and willingness. Someone might be financially ready but not mentally he is not. It might be that he needs to know one or two things about Bitcoin investment before jumping into it. However, getting little knowledge does not take long one or two days is enough so that shouldn't be an excuse. I also notice that many persons due to other failed investments they have done in the past still have this fear in them on investing into another asset like Bitcoin. Well, such persons should guided and mentored so that they can overcome the fear and start their investment.
Mental preparation for Bitcoin investment is just an excuse. If you are financially ready for Bitcoin investment and have basic knowledge, then you can invest without hesitation.
mental preparedness is not an excuse and from the standpoint of @Stablexcoin, his explanation makes a lot of sense as to why should be prepared before jumping right into investing in something he likely lacks some basic knowledge on. at the start of an investors journey, there is always the anxiety on whether or not one should invest in certain asset and when you don't have a strong resolve, even after investing, chances are that you might be forced to selling immediately there is a market downtime. that will not be the case if you are mentally prepared and understands the nature of the market condition and how that it can have effect on your responsiveness to the market condition.
even though at the start you don't have to give excuses of lack of knowledge as what is holding you back from investing, getting the necessary knowledge and being prepared that you are investing for the long term will see you through the early phase of doubt that might arise if the market fluctuates at some point in time.
To sustain your investment in the long term, you need to gain knowledge later, which is definitely after you start investing, and you should not delay investing for this knowledge. If you delay investing to learn more beyond basic knowledge, you are making a mistake and missing out on buying opportunities.
one thing that we should know about the stand of most persons when they are just getting started in their bitcoin investment is that anyone that is really ready to invest will certainly start investing even if they don't follow all ideal process and even if it takes them too long to know a lot of things that should normally help them start investing well. like you have said, and which is partly a similar opinion @Stablexcoin shared, what you just need is basic knowledge about bitcoin and then you can just get started. as long as the resource is available and you have a set out plan that works based on the peculiarity of your income flow, the rest of the knowledge can come pretty later while you have already started investing.
like the idea of setting out emergency fund and some reserve and back up funds, even though they are necessary for successful investment in the long run, a starter might not have the means to setting all of them in place before getting started but can just start whichever way he can while when he has gotten his stand as an investor, he can then find a way of sorting those kinds of things out. trying to set everything perfectly is a recipe for procrastination but then, you ought to be mentally prepared that your investment is for the long run and that you are not just coming in just to zoom off at no time.