When it comes to historic memorabilia items, the more personal it is the better if you're looking for pieces that are both coveted and valuable.
Whether it's a politician, a pianist, or a painter, personal items which give insight into a famous figures thoughts or creative processes are especially popular among auction bidders.
In terms of music memorabilia, recent popular examples include a letter written by Elvis to Colonel Tom Parker, his manager, in which he wrote: "Dear Colonel Tom, thanks and I love you like a father."
"Dear Colonel, Words can never tell you how my folks and I appreciate what you did for me. I've always known and now my folks are assured that you are the best, most wonderful person I could ever hope to work with. Believe me when I say I will stick with you through thick and thin and do everything I can to uphold your faith in me. Again, I say thanks and I love you like a father" - Elvis Presley in his letter to Colonel Tom Parker
By this point, Parker had only been Elvis's de facto manager for a month.
Yet years later, Presley said of Parker: "I don't think I would have been very big with another man. Because he's a very smart man" (as quoted from Peter Guralnick's 1995 book, Last Train to Memphis: Rise of Elvis Presley).
This letter sold for tens of thousands at Heritage Auctions in 2010 - a great example of how more personal manuscripts can prove irresistible to collectors.
From 'fatherly love', how about brotherly rancour - the type felt between former songwriting partners John Lennon and Paul McCartney following The Beatles' split in 1970?
Today, personal manuscripts can give collectors an insight like no other into rock 'n' roll animosity. Like this 1971 letter from Lennon to McCartney which was apparently never sent.
In response to a communication from McCartney, Lennon opens with: "I was reading your letter and wondering what middle-aged cranky Beatle fan wrote it."
Lennon goes on to announce his regret at accepting an MBE in 1965 as well as to complain about his wife's treatment from the other Beatles.
"I hope you realise what sh*t you and the rest of my 'kind and unselfish' friends laid on Yoko and me ... Of course, we changed the world - but try and follow it through - GET OFF YOUR GOLD DISC AND FLY! ... God Help You" - John Lennon writing to Paul McCartney in 1971
We've looked at a manuscript which captures musicians' thoughts.
But how about their creative processes? In the past, we've examined the popular of classical composers' music scores on the private markets.
But what if rock 'n' roll is more your thing? Well, if so, look no further than penned lyrics, which have proven to be among the most successful auction sales in recent times.
For instance, an original copy of John Lennon's handwritten lyrics to The Beatles' classic song "A Day in The Life" sold for $1.2m at a Sotheby's New York auction in June of 2010.
And handwritten lyrics to Lucy in the Sky with Diamonds sold for $237,000 at an auction in the United States in May 2011.
While nobody's paid $1.2m for a Sir Paul McCartney lyric sheet, a page of working lyrics for McCartney's song Maxwell's Silver Hammer did bring $192,000 at Christie's in 2010. The song is especially famed for its dark mix of a bouncy tune and murderous plotline...
Of course, those examples have sold but there are plenty of other rare examples out there. Here are some other rare examples of handwritten song lyrics which are currently for sale at Paul Fraser Collectibles...
Handwritten lyrics by Mick Jagger (PT274)
Handwritten lyrics to Hippy Hippy Shake by Stuart Sutcliffe (PT273)
Handwritten, signed lyrics by Phil Collins (PT275)