If you take action and forget to sit back every now and then to see what has been achieved, you might question at a later stage the "why" of your actions.
This satisfaction you gain from hitting the target is a key aspect of motivation.
If you are in business, use statistics to measure the impact of your actions, steps, strategies, etc.
With less substantial areas like love, happiness or life satisfaction results can be harder to measure. You can for instance give yourself a mark (between 0 and 100%) for the way you feel, and see how this mark evolves over time.
Measuring results wakes up a "competitive thrill". This is a positive force which keeps you awake and excited about your goals.
The key is to be aware of these dynamics and master them.