They work because they don't involve drastic changes - no big shock to the system.
Making sure that I stick to 1 (or less) teaspoon of sugar in my coffee is likely to make a difference over time as coffee and chai are two important drinks during the day. Those can add up quickly.
there are always surprises. My whole grain bun that I used for a grilled cheese sandwich has 4 g of sugar.
There goes a teaspoon...
Awareness is key:)