For example, doubling your effort in writing a book can have it go from okay to great, which likely brings much more than double the value.
This is one of the positive aspects of having fewer commitments on your plate. A negative aspect of having too much to do is that Many commitments bring a fixed amount of overhead, so keep the number of commitments low.
References
- Link to website, bibtex from Zotero or note with book/blog/etc summary