This is the danger, this is the pitfall, this is the reason traders fail.
When you postpone buying because you expect the price will continue to fall, you are a trader.
Don't look at the price, just buy when you can and only sell when you need cash and only as much as you need at the moment.
For over 20 years, I no longer invest almost all my money in one stock. The specific percentage varies, but it would take a very special situation to get me over 50% Not because I had a bad experience doing that, but because I manage risk differently now that my portfolio is much larger than it once was. Knowing and understanding risk/reward is the most important part of being a successful investor. The size of my largest position is dependent upon my analysis of risk/reward. Only in the most favorable situations will I let one position become well over half of my total. So, as the price drops, I can increase the size of the position in terms of percent of total. As a young man the calculation was somewhat different because I had more risk tolerance due to more available recovery time. Risk is only bad when it doesn't come with a corresponding reward and the measure of both of those things will change depending upon your life phase.
When TSLA dropped under $45 ($225) in 2019, I knew I was going to buy more which is why I started watching the price continuously. The bottom had fallen out, actually it had become a falling knife. I knew I wouldn't hit the exact bottom, but I also knew the pattern was very unambiguous in the short-term (which does happen from time to time). More likely than not, patience would pay off in such a situation. The old saying "don't try to catch a falling knife" really does have validity, if the knife is truly falling. Sure, there was a chance it would cost me some shares, but there was a much greater chance it would reward me with three or six times the number of shares that this strategy might cost me if there was an unexpected reversal. Considering I already had a sizeable position, that was a gamble I wanted to take, and I was well-rewarded by being able to double my position instead of adding considerably fewer shares. Had the price reversed prematurely, I would have immediately made my purchase, although with somewhat fewer shares.
When the price is dropping precipitously as it was in May 2019, patience can be a very good thing. I knew I would be buying shortly, I just didn't know how many I would be buying or how large of a percentage of my total it would be. The more it fell, the more I could buy for two reasons:
1) The relative value would be greater so it could be a larger percent of my total. This is risk management 201. It's also why the share price never enters into my appraisal of the actual value of the company.
2) More shares per dollar invested. This is basic math.
I also disagree with only selling as much as the cash you need at the moment. If you know you will need cash in a year, for a planned house upgrade (or any other large upcoming need for cash), and the stock price is extra strong, and has been for some time, it's wise to take some off the table in advance of your need for cash. This puts you in control of when you sell, and removes some of the volatility risk. I've often said that volatility is not risk for a long-term investor, but that always comes with the qualifier that you will not be required to sell during low points (like right now). Because, if you know you are going to have to sell in a year, you are no longer a long-term investor, at least not with that portion of your portfolio. That is capital that is subject to short-term investing rules. In short-term investing, volatility
is risk and it is very real risk.
Discipline while following these principles is what has allowed me to be a very profitable long-term investor with minimal stress and time spent trading or worrying about my positions which frees up time an energy to spend on the more enjoyable and profitable side of investing, learning about new technologies that are becoming ripe for commercialization, familiarizing myself with the companies that may benefit the most and how new developments impact my holdings.
Long-term investing does require a certain amount of discipline to excel, but it doesn't require extreme intelligence or knowledge beyond the application of logical first principles thinking and some common sense. Most people who under-perform are making very basic errors of judgement, whether it be due to letting emotions guide their thinking process, greed or simply illogical thinking. It doesn't need to take a lot of time either, although spending more time being more familiar with the actual subject of your investments can increase returns by increasing your ability to more accurately appraise risk/reward ratio of any given investment. Of course, there comes a point of diminishing returns. For example, even Elon Musk, who is more intimately familiar with Tesla's potential than any of us can hope to become, doesn't know where the share price will be in 10 years (other than it will be a lot higher than it is right now). How much higher depends upon too many unknowns to say with certainty that the 5-10 year returns will be mind-blowing but I have trouble seeing credible scenarios in which at least s
ome of Tesla's initiatives, beyond automaking, don't become insanely profitable.