"I'll explain later" is a phrase that Moffat jokingly came up with when making The Curse of Fatal Death, which ironically resulted in the fatal death of his writing ability as he has since acquired it as a mindset for his storytelling ever since
Series 6 The Big Bang Silence in the Library. Literally every finale of his run has the Doctor or someone else recapping all the unsolved mysteries of the series (many of which would remain unsolved forever, btw) before I am the Doctor begins obnoxiously blaring out, accompanied by the image of Matt Smith spinning around the TARDIS console like a retard and shouting "DOCTOR WHO??????" at the top of his lungs.
Notable examples of "I'll explain later" Edit
Ones which are still unresolved are in bold. Ones that are sorta solved-ish kinda but not really are in italic.
- Who is River Song?
- Who blew up the TARDIS and how?
- Who was in the astronaut suit?
- Who was the little girl?
- Who's the eye patch lady?
- Is eye patch lady dead?
- What are the fields of Trenzalore?
- What is the Doctor's name?
- How will the Daleks remember the Doctor?
- Why can't the Doctor go back to 1930s New York?
- What did the Doctor do with the stray Angel?
- How did Strax come back to life?
- Who is Clara?
- Why did Clara and Oswin have different names?
- Who thought bringing back the Great Intelligence was a good idea?
- Who is the War Doctor?
- What happened to the human/Zygon plot?
- When will the Doctor find Gallifrey?
- How did the Doctor not age from the 200 years he spent travelling in Series 6, yet aged from a mere 300 years on Trenzalore?
- Where did Capaldick get his face?
- Who is Missy?
- Is Capaldick a good man?
- Is Orson Pink a product of Clara and Danny fucking?
- Why is Capaldick suddenly anti soldiers again?
- What did Clara do with the resurrected middle eastern kid?
- Are the Doctor and Clara still dreaming?
- What is the Hybrid?
- Why did Davros' kiddie memories of the Doctor only just come up now?
- Wait, why did Harry Sullivan make a gas that would kill the Zygons? I thought he was a doctor, not a genocidal scientist.
- Why did the Time Lords employ Ashildr to get the Doctor to them?
- Why are the Time Lords asking the Doctor to confess about the hybrid if he doesn't even know what it is?
- How did the Sisterhood of Karn get to Gallifrey if they clearly weren't on Gallifrey in previous appearances?
- Where did Rassilon go?
- Will Moffat ever become a good writer again?