for something I sold on ebay.

The same day I had a bunch of payslips in my drawer at work. So put the payslips in the envelope and took them home later.

As soon as I got home didn't think threw the item in the envelope and dropped in the post box only to realise that I left the payslips inside

I had to ask the person to send them back to me

The 'your mum' reply is most welcome.