Here is my 100% Achievement Guide for Tell Me Why
This is the longest achievement to gain but still is rather easy.
When you enter the store and grab items, Tessa will then enter, have a chat with you and head into her office.
From here, go to the cleaning products, watch 2 memories then you have to decide on which memory you want to choose (no answer is wrong but can improve or deprove your relationship with Tyler).
Once you have chosen, go into the office and talk to Tessa and choose "Your Fight With Mary Anne".
Once this convo over, go talk to Tom on the till and choose "Do you remember that one song?"
Next, there are two memories in the store to find, one infront in the first aisle..
Te second one is right by Tessas office in Aisle 3.
Once these two have been found, go into Tessas office and on her computer.
Choose the 2nd email "Family Alliance".
After you quit out you should see a symbol in the top right hand corner.
Now go into the metal cabinet right of Tessa and find the black book (Also has a goblin Collectible in here). Skip to Mary Annes page (big long list of debt) and then quit out. (SHOULD see another symbol top right)
Now talk to Tessa again and make sure tk choose these options..
1. We Remembered Details
2. October 2004
3. You Told Her About The Camp
4. The Virute Seekers Youth Camp
If you did all of the above the achievement should unlock when the cutscene ends.
If you prefer to see a visual, go to 1:23:40 to see the start and all of this being done.
Hope this helps!