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It's really important for beginners to fully understand bitcoin before they start investing in it. They should know what they want to achieve and the strategies that go along with the type of investment they want to make. Also, it's important to know that bitcoin is not something you can make quick money from so it's better to have realistic expectations.
I agree that it's not always best to only buy bitcoin when the price is low. Instead it's important to be financially ready to buy whenever you can no matter what the market is doing.
No need, I don't think it's mandatory. You don't have to be an expert and have a technical understanding of bitcoin to be able to invest in it, but you should understand how the market works and how bitcoin has value. What you need is how to buy, how to sell, a buying strategy and when to sell and how to manage your assets. The technical understanding you need is analysis, not something other technical like networking, development, mining, etc.
As time goes by, you can learn technical things that support your further knowledge about bitcoin. But you don't have to be an expert to invest, that's the point. Having a budget, establishing a plan, considering risks, managing assets, and self-control are important to get started, but don't complicate things unnecessarily.