I think one of the advantages of starting with small amounts diverted to investments on each paycheck is that the market movement is much less evident. After 6 months you aren't hyper conscious of how much you put in vs. what it is now, while if you put in 10k in May, you are more likely to remember it was 10k.
Since I'm putting in money all the time, I don't track investment amount vs. growth, I just track the amount in the accounts. I remember the first time I was down $900 even _after_ I put in ~$1000 for the month. I plugged my nose, closed my eyes, and put in another $1000 the next month, and then the month after that, and then my balances were up on the year.
In 2015 for months my balances were basically flat, despite dropping in money (I did end up, but I didn't calculate the % that was growth vs. additional purchases). In 2016 my balances are down, again despite dropping in money in both lump sums and on paydays.
Each year, the amount that I am dropping in is a lower proportion of the balance, so I have less control over the month to month number, but by tracking and working through it for years, I've been able to mostly inure myself against the swings. I'm trying to train myself for when I'm closer to the target number and looking to pull the trigger.
