Of course, you can learn things, but it would be more productive to observe them when they are free.

productive 是由名词 product（产品、成果）加上形容词后缀 -ive 构成的形容词，字面意思是"能产生成果的"。在这里引申为"有效率的、富有成效的"。 productive 强调能够产生实际效果或成果，比单纯说"有效"更强调产出和效率。