Social media sentiment, or the overall emotional tone driving a conversation, has never been easy to predict.

In the frenzied online world where opinions are given ferociously and freely, the overall mood and perception of a subject and how it should be treated can shift in the blink of an eye.

This capriciousness surfaced several times in the past week, most notably in the case of outgoing Transport Minister Lui Tuck Yew.

While his announcement to leave politics came as a shock to many, it is perhaps even more startling to see how social media reacted.

Barely more than a week ago, many netizens would have had no qualms taking to the Internet to heap blame on Mr Lui whenever a train broke down.

But that mood seems to have shifted after news of his impending exit. Was it a case of not knowing what you'll miss till it's gone? Or was Mr Lui humanised after it is known he's about to leave his official post? Or did the "silent majority" choose to speak up?

In an interview with The Straits Times, even Mr Lui seemed surprised. Within a day, he received a flood of e-mail thanking him for his work, and one in five expressed regret for criticising him or not speaking up for him online.

Many members of the public, such as SGTrains, a Facebook group of transport enthusiasts, also posted their farewells.

A 2006 report on his humble beginnings in a rental flat became one of our top stories this week, garnering more than 150,000 page views within a few days.

This phenomenon stood in stark contrast to business owner Emma Lee. The 29-year-old was thrown into the spotlight after broadcast crews at the National Day Parade featured her in the media coverage several times.

Netizens scrambled to find her identity. Ms Lee says she received hundreds of friend requests through her various accounts.

The attention, however, turned sour when some realised she is not Singaporean.

But being a foreigner proved to be no barrier in another case where a Ugandan woman, disfigured by an acid attack, sought help to restore her sight.

An online donation page set up by three Singapore expatriates for Ms Namale Allen to come here for treatment raised more than $50,000 within two days.

Many donors were reportedly Singaporeans.

While there is no hard and fast rule to navigating social media, perhaps one tenet holds doubly true: Expect the unexpected.

CHILD PREDATORS ONLINE

Is it easy for paedophiles to get in touch with children via social media? Disturbingly so, going by this viral video last week.

YouTube film-maker Coby Persin posed as a 15-year-old boy, befriending three young girls on Facebook and asking them out.

The girls, who are between 12 and 14, readily agreed to meet and snuck out of their homes when they thought their parents were not around. Luckily for them, their parents were in on the plan and promptly told their daughters off. The video, which was uploaded on Monday, garnered 27 million views.

TENSION ON TINDER

Tinder went into a Twitter tizzy last week after a Vanity Fair article on its users was posted online.

The article implied that the app heralded the "dawn of the dating apocalypse" for the way it is being used and its alleged promotion of a polyamorous lifestyle.

Tinder launched a slew of tweets from its official account, criticising the report.

The backlash?

Many netizens seemed to support the article's writer, Ms Nancy Jo Sales, instead.

SOCIAL MEDIA MARKETING GONE AWRY?

Celebrity Kim Kardashian got into trouble for posting an endorsement for a morning sickness drug on her Instagram and Twitter accounts, without mentioning the associated risks. Needless to say, the United States Food and Drug Administration was not amused.

It sent the drugmakers a letter, asking for the posts to be taken down. One Twitter user wrote in response to her tweet: "I think you need to research a product before you start promoting for money..."