Why does splice need an index of [0] at the end of this statement to store the value of the spliced item?

I have recently discovered a solution to a splicing issue I had where I could not access the value of the spliced object from an array of objects I have, it would show it as "undefined" when I tried to print the spliced object like this -

function QuoteSplicing() {
    //splice quotes from the original array and push them into a new array.
        spliceQuote = quotes.splice(quoteObject, 1);
        quotes2.push(spliceQuote);
        console.log(quotes);
        console.log(quotes2);

        if(quotes.length == 0){
            quotes = quotes2;
            quotes2 = [];
        }

        retu spliceQuote;
}

I then wrote a function that printed the spliced quote but it would show up as "undefined."

I fixed my QuoteSplicing function by adding an index value at the end of the splice statement -

function QuoteSplicing() {
    //splice quotes from the original array and push them into a new array.
        spliceQuote = quotes.splice(quoteObject, 1)[0];
        quotes2.push(spliceQuote);
        console.log(quotes);
        console.log(quotes2);

        if(quotes.length == 0){
            quotes = quotes2;
            quotes2 = [];
        }

        retu spliceQuote;
}

I have the fix after looking around, but I am trying to understand the why here as I feel it is important, how does adding the [0] index to the end cause the spliced quote to not show up as undefined anymore?