Some times you may encounter this. You are trying to double click the texts you added again and again but the layer will not allow you to edit the text.

It's simply because, instead of the text, the text layer is selected and you are trying to double click again.

Here is how you fix this if you ever encounter such issue:

1. On the above figure, having those angles and pointers around the blue dashed rectangle means the text layer is still selected. Click anywhere on the background image outside of the text layer.

2. Now directly double click on the text layer. You will see the text is selected this time and your keyboard cursor will start blinking at the end of the text which means, the text is selected this time.

3. Now you can start editing the text. 

Here are some cool text editing tips:

A. Press and hold Alt key then press A to select the whole text and start typing or paste your own text.

B. Use the Backspace key to delete the the texts from right to left.

C. Use combination of Left and Right Arrow Keys in to go to the specific word or part of text then press and hold Shift and use Left or Right Arrow Key to select any specific word or part of text. Then simply paste or type in your text.