I decided that now is the time to start doing the things that really interest me and I find important. It was in the 10 years of the MacArthur grant that I began working on my first book... and I began putting more work into environmental history.

Diamond is describing a pivot from externally driven obligations toward intrinsically motivated work. The “now is the time” framing suggests a deliberate decision to prioritize projects he judged meaningful—especially long-form synthesis (a first book) and the then less mainstream field of environmental history. By tying this shift to the security and freedom provided by a MacArthur Fellowship, the quote highlights how time and financial independence can enable intellectual risk-taking: pursuing interdisciplinary questions, investing in research that may not yield immediate professional rewards, and building a new scholarly identity. It also implies that major contributions often arise from sustained, protected time rather than short-term productivity pressures.