Excess contributions tax harshly penalise those who exceed their contributions cap. The excess contributions tax levies a tax of 46.5% on any contributions above your cap. You are personally liable for the tax, not your superannuation fund, although in some cases the tax can be paid from the superannuation fund.
If you use the bring forward option and make 3 years worth of contributions in one year, and miscalculate, the resulting contributions tax can be devastating.
The Government has introduced changes that allow individuals who breach the concessional cap by up to $10,000 to have these excess amounts refunded to them and included in their own assessable income, rather than in the superannuation fund.
It is very easy to inadvertently, get the timing of payments wrong (the contribution is made on the date the payment is received by the fund), are unaware of the implications of salary sacrifice agreements on your super, or simply lose track. The definition of a contribution is wide. For example, if your life insurance premiums held within your fund are paid by your employer, then the premium paid would count as a contribution. Personally meeting your fund expenses could also be counted as a contribution. For example, if you pay for the fund's accounting fees (rather than the fund) it's considered to be a contribution.