Why should I make a copy of a context for goroutines inside handlers?

I recently started rewriting some of my Python services in Go to speed them up and came across this section of the gin documentation:
https://github.com/gin-gonic/gin#goroutines-inside-a-middleware

So I understand the instructions, but I'm trying to understand why? What is the significance of making a copy, and what problem is introduced if I do not make a copy of context for goroutines within handlers?

Gin-gonic is async itself which makes it great.
If you are using concurrency within your handlers it's very likely you will face situation when Context, which is struct goes

• outdated since it's holding the data from each request (parameters, keys protected by mutex)

• empty, which will cause a fallback to default Context

here's how it looks like:

type Context struct {
writermem responseWriter
Request   *http.Request
Writer    ResponseWriter

Params   Params
handlers HandlersChain
index    int8
fullPath string

engine       *Engine
params       *Params
skippedNodes *[]skippedNode

// This mutex protects Keys map.
mu sync.RWMutex

// Keys is a key/value pair exclusively for the context of each request.
Keys map[string]any

// Errors is a list of errors attached to all the handlers/middlewares who used this context.
Errors errorMsgs

// Accepted defines a list of manually accepted formats for content negotiation.
Accepted []string

// queryCache caches the query result from c.Request.URL.Query().
queryCache url.Values

// formCache caches c.Request.PostForm, which contains the parsed form data from POST, PATCH,
// or PUT body parameters.
formCache url.Values

// SameSite allows a server to define a cookie attribute making it impossible for
// the browser to send this cookie along with cross-site requests.
sameSite http.SameSite

}

In order to foresee such issues and race conditions - you must use Copy whenever your handlers are using go concurrency

here's a quote from gin-gonic repository:

// Copy returns a copy of the current context that can be safely used outside the request's scope.
// This has to be used when the context has to be passed to a goroutine.