Wpf textblock text binding not updating
The second Text Box uses the Lost Focus value, which is actually the default for a Text binding.
It means that the source value will be updated each time the destination control loses focus.
As you can see, each of the three textboxes now uses a different Update Source Trigger.
The first one is set to Explicit, which basically means that the source won't be updated unless you manually do it.
In the ancient and cruel world of WPF you might want to populate a Text Block with a string which will contain data from different sources.
Just make sure that you don't update the source value more often than you actually need to.
The third and last Text Box uses the Property Changed value, which means that the source value will be updated each time the bound property changes, which it does in this case as soon as the text changes.