Tedomari is Worth Double
This proverb applies to the final gote (or reverse sente) of the game, or the final gote which leaves only miai. It has to do with the fact that the normal, expected gain from making a play with gote is 1/2 the miai value of that play. But the gain from the game tedomari is the full miai value of the play. It gains twice as much, on average, than if it were not tedomari, so you can consider it as being worth double its face value.
Here is the rationale. Suppose that you make a play with gote that gains N points (Its miai value is N), and it is the largest such play. Now your opponent has sente. How much is sente worth? It might be worth nothing, or it might we worth up to N points. On average, we expect it to be worth N/2 points. So our expected gain from making our play and giving up sente is N - N/2 = N/2 points. But if our play is the last gainful play in the game, giving up sente costs us nothing, so our expected gain is N points, twice as much as our normal expectation.