Wrong.
Planning something to do on a certain date with a girl that is into you, and not telling her what it is, will have her thinking about it all the time trying to figure it out. She'll think "omg is it something I hate!" or "Omg what if it's something I love!" and go back and fourth on it until she thinks she has it figured out. She’ll also be thinking about everything you guys did together in the last month for clues as to what it might be.
Emphasis on she is already into you
It's all about how you execute it.
You don't sit there and say Lets go out on the 2nd, but oooo i'm noooot gonna ttelll you where, it's a guuuunnnnna be a surprIIIIIIse.
and be all sappy and stupid.
You say "Don't make any plans for this weekend"
She'll ask why
and you say "[insert your own natural evasive answer here]"
I've done it, works well.
they even might think is all cornball and stupid at first! And even say so, but the reaction AFTER the fact is them thinking about it all the time.
If you think something is AFC, or you think something will not work, and you have no personal first had experience trying it or an experience to reference where it failed…then your opinion is worthless. Further, anyone with any amount of experience knows that all women are different to a certain degree and some will respond very well to something like this where some wont. What people who want to be productive should be doing is posted about how something like that has or has not worked for them in practice and why.
*shakes head*