diff --git a/README.md b/README.md
index 7bfa490dd..43aba314f 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,23 @@
 libent is a cross-platform wrapper around `getentropy(2)`. It exports
 one symbol, `ent_getentropy`, which expands to `getentropy` if the
 latter is available. Otherwise, it tries to use the next best source of
-entropy -- /dev/urandom on *nix, BCryptGenRandom on Windows.
+entropy — `/dev/urandom` on *nix.
+
+### Why?
+
+`getentropy` is the wave of the future. It's the correct API for
+generating small amounts of entropy to create cryptographic keys or seed
+PRNGs. It's good and reasonable and true, it's on Linux, *BSD, and OS X,
+and it only took us fifty years of UNIX to get here.
+
+Sadly, it only just arrived, so nobody has it yet. It didn't land in
+Linux until glibc 2.25, which seems to only have made it into Debian 10.
+
+Once `getentropy` is everywhere you care about, you can just do a
+s/ent_//g on all the call sites and discard this shim.
+
+Admittedly, 90% of the motivation behind this was to fix the randomness
+shim in [Urbit](https://github.com/urbit/urbit).
 
 References:
 * [OpenBSD getentropy](https://man.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man2/getentropy.2)