A lead is someone who is not a customer yet: a submitted form, a phone call, an introduction.
Only three states
New, lost, converted — that is all. The list is deliberately short; it used to be longer, and in practice nobody read the middle states the same way.
If you need more detail to work a lead, that belongs in a note or a task, not in a new status.
Converting creates a new record
Converting a lead creates a customer and copies the lead's details into it. The lead itself is not deleted — its status becomes converted and it stays where it is.
So you end up with two records, and that is correct: the lead is the history of where this person came from, and the customer is what invoices and orders attach to from now on.
The conversion is a copy, not a live link. Editing the lead afterwards does not change the customer record.
Do not expect complete data
Unlike a customer, a lead can be nearly empty. One that arrived from a website form may have only a name and a way to reach them.
That is not missing data — it is the reason leads exist: somewhere to keep an incomplete prospect until they are worth converting.
Take the source seriously
Every lead records where it came from. It is the one field that later answers "which channel actually brings customers", and unlike a name or a number it cannot be reconstructed after the fact.
Delete means trash
A deleted lead goes to the trash, not out of the system. If a lead has "disappeared", look there first.