Earlier I traded a channel much like this one and lost. Zooming out you can see that the channel I've drawn in blue is really just a subset of a wider channel.
Now that today's low point has appeared, you can see that the blue channel is in fact the lower half of a wider channel.
To avoid this mistake:
Look for a swing low below the current channel. If it exists, draw a line from that swing low parallel to the known channel. Now you can use that line when setting up trades.
The same idea could be applied to the top side of the channel as well.