I'm talking about the lowest of the low here - an end-fed wire on the ground. On transmit it's almost a dead loss. Like short circuiting most of your signal to earth. On receive it's a different story. That's because we're after not so much signal strength but signal to noise ratio. Here a new antenna that reduces the desired signal by 10 dB but undesired signals and noise by 15 dB is a winner due to an overall improvement in reception quality.
Enjoy these articles and videos on what antennas on the ground can and can't do.
* KK5JY's loop on ground antenna
* 40m SSB with a wire antenna along the ground.
* HF WSPR with a wire antenna along the ground.
PS: For some much better antennas try some from Hand-carried QRP Antennas. Available in electronic and paperback form (some countries) this well-reviewed book is a popular read amongst hams who go portable.