"When you are young, beginning new projects is easy and finishing them is hard. As you grow older, beginnings get harder, but finishing gets easier. At least, that has been my experience. I think it is true of anyone of at least average intelligence, creativity and emotional resilience. The reason is simple.
When you are young, the possibilities ahead of you, and the time available to explore them, seem nearly infinite. When you try to start something, the energizing creative phase, (which comes with internal brain-chemistry rewards on a fast feedback-loop), gives way to exhausting detail-oriented work, maintenance work, and unsatisfying overhead work. You need to get through these to bank distant external rewards (money and such) that only come with completion. It is then that you are most vulnerable to the allure of exciting new beginnings. So you abandon things halfway. You bank the internal rewards of beginning, but not the external rewards of finishing.
But with age, this changes.
As you grow older, the history of a few completed projects and many abandoned ones in your past starts to loom oppressively in your memory. The early internal rewards of many beginnings are now a distant memory that offer no pleasure in the present. The external rewards of completed projects, which tend to continue to yield dividends (such as completed degrees, financial rewards) loom larger all around you: wealth, strong relationships and perhaps most importantly, an earned ability to see the world differently as the result of having been through many completions.
When a new opportunity opens up at 35, you evaluate it differently than you did at 25. You are able to estimate how long it will take, what the journey will feel like, what the early pleasure and distant pain will feel like, and what getting it done will feel like. You are able to react psychologically to the whole prospect in the form of a narrative that extends beyond the finish line, as a systematic leveling-up of your life. You see the transient pleasures of beginnings diminish to nothing in the far future and the enduring rewards of finishing as a steady source of dividends extending out beyond the horizon."
- http://www.tempobook.com/2014/01/13/when-finishing-is-easier...