# EVENING

_Systematic Investing . 2026-05-31 . By Tanmay Kurtkoti. Educational, illustrative, not advice._

A friend spent his entire Sunday comparing two large-cap funds. Spreadsheet open, expense ratios lined up, five year charts side by side. He wanted to know which one to pick.

I told him he was sweating the small decision and skipping the big one.

The big one is the split. How much equity, how much debt, how much gold. Brinson and his co-authors put numbers on this back in 1986, and the finding has held up through every market since. The mix you choose explains roughly ninety percent of how much your portfolio's returns swing around over time. Which specific fund you drop into each sleeve is the smaller lever, not the larger one.

Now the part the brochures quietly mangle. That ninety percent is not "ninety percent of your return comes from asset allocation." Ibbotson and Kaplan cleaned this up in 2000. It is about variability, how bumpy the ride feels over the years, not about where the magnitude of your return came from. Look across different funds instead of across time and the split explains closer to forty percent of why yours landed differently from mine. On average across everyone, the policy mix accounts for roughly the whole long-run level, because active picking is close to a zero-sum game before costs.

The cleanest way to see it is to hold the index in every sleeve, so the picking is identical, and just move the mix. All equity returns about 10.4 percent and makes you sit through a 52 percent drawdown to get it. A 40 40 20 mix returns about 8.5 percent and never falls more than 18 percent. Two points of return between them. Thirty four points of drawdown. Same holdings. The split did all of it.

So the honest version. You can spend a weekend on the pick and one Tuesday afternoon on the split. The Tuesday afternoon decides more. The brochure sells the pick. The math pays the mix.

What your asset allocation actually decides: