The S&P/ASX 200 Index (ASX: XJO) is on course to end the week with a gain. In afternoon trade, the benchmark index is up 0.25% to 8,096.5 points.

Four ASX shares that have failed to follow the market higher today are listed below. Here's why they are falling:

Brambles Ltd (ASX: BXB)

The Brambles share price is down 2.5% to $18.01. This follows the release of an investor day update from the supply chain solutions company this morning. Analysts at Goldman Sachs weren't overly impressed. They said: "Guidance for 4-6% sales growth and 8-11% underlying profit growth with US$750-850m of pre-dividend free cash flows is unchanged. All these metrics are broadly consistent with our expectations and continue to point a relatively seamless transition to BXB's 'normal' growth algorithm after a period of elevated growth." Goldman has a sell rating and $15.90 price target on Brambles' shares.

Guzman Y Gomez Ltd (ASX: GYG)

The Guzman Y Gomez share price is down 6.5% to $38.50. This is despite there being no news out of the quick service restaurant operator. However, it is worth noting that its shares rallied strongly this week after being added to the ASX 200 index. This left them trading on eye-watering earnings multiples. It's possible that some investors have decided to lock in gains now. Alternatively, there's potential for short sellers to be taking a look at the company now its shares are being added to the benchmark index.

Liontown Resources Ltd (ASX: LTR)

The Liontown Resources share price is down 4% to 68.5 cents. Investors have been selling Liontown and other ASX lithium stocks on Friday. This seems to have been driven by profit taking from some investors after big gains over the past couple of sessions. For example, Liontown shares remain up 13% this week despite today's decline. This strong gain has been driven by optimism that lithium prices have reached a bottom.

Medibank Private Ltd (ASX: MPL)

The Medibank Private share price is down 3% to $3.71. This follows reports that hospital giant Healthscope has won its war with Medibank and other private health insurers. According to the AFR, Medibank Private, NIB and HCF have agreed to out-of-cycle funding payments in the "tens of millions of dollars" for Healthscope. This follows a warning from Healthscope that it would be forced to close hospitals without funding relief from insurers.