Well, it relies on what is your strategy and to your desires every person has their own decision and situation. We never know when the period the money will be needed. When I purchase a coin, I usually set or plan an value when I want to retail it. The amount of the coins depends on the market cap and the total supply and the demand of the currencies. There is particular opinion to set your prediction and the goal, as long the result is positive profits, then it's satisfactory. If you are a trader, don't be impatient and set your targets according to your plan. When you reach your objective, then sell.