Some people new to Go get confused when searching for an option to subtract a `time.Duration`

(e.g. 24 hrs - to derive yesterday) from a certain time. When looking at the `time`

package one sees only an option to "add" time, but not really to "subtract" time. There is a `time.Sub`

function, but it takes a `time.Time`

and returns the elapsed `time.Duration`

instead. When it comes to subtracting a duration from the given time, there does not seem to be an available option. Or does it?

Recall that in arithmetic, subtraction is the same as addition using a negative prefix. Thus deriving "this time yesterday" from "now" is as easy as:

```
now := time.Now()
fmt.Println(now)
fmt.Println(now.Add(-1 * time.Hour * 24)) // This time yesterday
```