The best way to learn how to do something is to do it, whether it's riding a bike, playing the piano, writing essays, or doing research. Learning by doing also makes you a better learner by encouraging reflection.
Reflection is critical to learning how to learn (metacognition) and being a successful self-directed learner. Being a 'learning worker' keeps us relevant and valuable in the 21st century workplace.
'To teach is to learn twice.' (Joseph Joubert, 1883)
Research consistently shows that teaching others enhances your own learning in a powerful way. Peer assessment also leads to a better understanding of assessment criteria, a better ability to self-assess, and therefore improvements in one's own performance.