a tsql question

I can select records with the following statement -

select [id], [location], fn as 'firstname', ln as 'lastname'
from dbo.mytable
where fn like 'Mike%'

I need to change to the following query, why I cannot select any record?

declare @ttt varchar(10)
set @ttt = '''' + 'Mike' + '%' + ''''
--print @ttt
select [id], [location], fn as 'firstname', ln as 'lastname'
from dbo.mytable
where fn like @ttt

when I print  @ttt, it has the value 'Mike%'. I'm wondering why I cannot select any record after I replace 'Mike%' with a variable having the same value in the where clause.

Please help. Thanks.