If you doubt this then attempt, right now, to be happy in the future. It is
impossible. You can ONLY be happy in the present since the future does not exist yet.
You may be happy IMAGINING a future, but you are imagining it in the present.
You may say ‘I am not in happy circumstances right now’ or ‘If I had more money, or was
in a good relationship or….yada yada yada…. The truth is you can have an attitude
of happiness, even if it is out of commission for a short while due to circumstance
(such as a death/injury in the family, not because your nail broke).
If you can’t find something to be happy about today, what makes you think you will find
something to be happy about tomorrow?