It all depends on what type of buyer you are ?
If you are a long term buyer then you can start buying in split on each lower rate, so that his buying rate will be averaged and fix the term of time you are thinking of holding it and target of selling price, so that when u achieve it you should be able to sell it.
If you are a short term or trader then when ever their is a correction in market, you can start buying as after correction surely market will go up and you can start taking profit.
Good point and people just need to know there intentions before putting on some actions since if we don't know on which of that things we are unto for sure we be disturb for every movements of the market since we don't put any target plan on our trading plans. If people could only define first before going to trade if they are for long term or short term for sure they can stick on the game plan they might set for theirselves.
The disturbing of your strategy is one of the biggest reasons why people end up losing money. If you do not have a clear goal and know what you want to do way before you do anything, then you are going to most probably lose money (aside from few lucky shots in high bull periods).
However, if you have a plan, you know what you want to do, you put aside enough money to exercise that plan and you are ready, then you could follow that and most usually come out on top. Doesn't mean that first system would always lose, like I said it could win on some certain high bull periods, also doesn't mean second will always win, sometimes in bear periods you may have to wait longer than usual, or some people even sell and get out.