When trading, there are certain factors that you simply cannot control. You are only one trader out of maybe tens of thousands, who may be trading a particular stock or instrument - each with their own rationale, objective, timeframe etc. To participate in the market, you have to accept this, and accept that you can lose on any position you may take.
I've posted before here about 'controlling the controllable'. The main dangers to your longevity as a trader start to occur when you lose control of those factors. This mainly manifests itself in the following ways:
a) Overtrading - being in positions that are too large relative to your current equity levels;
b) Self-sabotage - for example, overriding your pre-determined stop level on a position, which then goes further against you. This means that, instead of taking a small loss per your system rules, you are now stuck in a position with a much greater loss.
In these cases, you are no longer in control - the individual stock or market you are trading becomes in control of you. When this occurs, you need to regain control, as soon as possible. If it means exiting your position(s) and suffering a major drawdown, then do it. Don't risk that loss becoming even larger.
When you are out of control, then you cannot think straight. You will become paranoid and will fret over every price movement affecting your positions, and therefore your profit or loss. For example, if you are trading a position that is too large relative to your equity, you will become prone to taking profits way too early, for fear of losing them. Alternatively, if that position goes into a loss, you will hang onto the trade (even if it breaches your original stop loss level), in the hope it will recover.
Most trend following methods attempt to 'systemise' as many factors as possible in the trading process - the trader can determine or pre-set the specific rules for entries and exits, stop placement, what markets to trade etc. When used in conjunction with prudent risk management, then you will have all the bases covered.
This should lead you to avoiding losing control of your trades and your emotions, and eliminate making irrational, portfolio damaging decisions. Then it is simply a question of having the confidence and discipline to adhere to your rules.
To become successful in this game, you need to remain in control at all times.