Here is a paradox. It is pretty easy to predict the voting patterns of new Supreme Court justices. But it can be exceedingly difficult to predict the votes of justices in specific cases — which means that it can be difficult as well to predict how those cases are going to be decided.
When President Bill Clinton appointed Stephen Breyer to the Supreme Court in 1994, those who knew Breyer's work knew that his voting patterns would be moderately liberal — more centrist than those of progressive heroes Justices Thurgood Marshall and William Brennan, but to the left, for sure, of Justice Antonin Scalia.
And when President George W. Bush appointed John Roberts as chief justice in 2005, it was clear, from Roberts' record, that his voting patterns would be moderately conservative — distinctly more conservative than those of Breyer, but distinctly less so than those of Scalia.
Something similar can be said about every Supreme Court nominee over the last half-century.
At the same time, the court is capable of big surprises. For example, many experts did not predict that in 2015, the court would rule in favor of same-sex marriage; that in 2020, it would strike down President Donald Trump's decision to repeal President Barack Obama's Deferred Action for Childhood Arrivals program, designed to protect some unauthorized aliens from removal; or that, in the same year, it would interpret the Civil Rights Act of 1964 to forbid discrimination on the basis of sexual orientation.
Indeed, a careful effort to test whether legal experts are good at forecasting the decisions of the Supreme Court found that such experts were right just 59.1% of the time.
That's better than flipping a coin — but not a lot better.
Judge Amy Coney Barrett's background shows unmistakably conservative inclinations, and it is a good bet that she would count, broadly speaking, as a conservative justice. But would she vote to strike down the Affordable Care Act, the 2010 health care law widely known as Obamacare? Would she vote to overrule Roe v. Wade, the 1973 ruling that women have a constitutional right to have an abortion? To forbid any and all affirmative action programs? Would she take a strong stand against gun control laws? Would she give more protection to commercial advertising?